|
|
|
|
|
|
|
|
Hard Photodisintegration of a Proton Pair (Strauch, Berman) A series of high-energy, hard-photodisintegration experiments of the deuteron have been performed in order to study the dynamics of the transition from the hadronic to the quark-gluon description of the strong interaction [Nap88]. At present, it appears that hard photodisintegration is an intractable problem in meson-baryon theories, and that the quarks are the relevant degrees of freedom, but they cannot be described through perturbative QCD (pQCD). Several non-perturbative quark models have been formulated, and are in need of further testing. The work on deuteron photodisintegration can be extended to hard photodisintegration of a pp pair in the 3He nucleus [Bro03]. We are participating in JLab experiment E03-101, which will measure both the energy dependence at qcm = 90o at five different photon beam energies for Eg = 1.6 - 5.0 GeV and the angular distribution near 90o CM for the hard photodisintegration of a pp pair in 3He [Gil03]. The goal of the experiment is to study new features predicted by [Bro03]: the main prediction, in contrast with low-energy observations, is that the pp breakup cross section is not much smaller than that for pn breakup. Further, in some models, the energy-dependent oscillations observed for pp scattering are predicted to appear in the g3He ® pp+n reaction. Such an observation would open up a completely new field of study: color-coherence phenomena in hard nuclear reactions. It is also demonstrated in [Bro03] that, in addition to the energy dependence, the measurement of the light-cone momentum distribution of the recoil neutron provides an independent test of the underlying dynamics of hard disintegration. Our anticipated results are shown in Fig. 7.
Figure 7. Simulated results for the qcm = 90o excitation function for g3He ® pp+n. The absolute normalizations of all the calculations shown are either fixed from the theory or fixed from the gd ® pn data: Hard-Rescattering Model (HRM, hatched area); Quark-Gluon-String Model (dashed); Reduced-Nuclear-Amplitudes Model (dotted). The figure is taken from [Bro03]. The points shown are the expected results for JLab Experiment E03-101, if the cross sections agree with the predictions of the HRM.Our CLAS data on the g3He ® ppn reaction [Nic03a] covers an energy range up to about Eg = 1.5 GeV. Thus, these data only begin to reach into the scaling region. However, they complement the expected data from E03-101 and make possible the comparison of hard pp and pn photodisintegration over a much wider energy range. These data are currently being analyzed with this objective in mind. |
|
This site is best viewed in Internet Explorer 6.0 or higher.
Send mail to
Web Master with
questions or comments about this web site.
|
